I'm using Gimp 2.6.12 on Ubuntu 12.04. It worked fine until a couple of days ago. This might or might not be relevant, but in the meantime, I tried to plug in my usb photo scanner but since it was not recognized by SimpleScan I didn't continue to bother (will do later).

So now I start Gimp and load an image (image type doesn't matter). The image is loaded fine but as soon as I attempt to use any tool by clicking onto the image, the entire screen goes black and for a very short time, some error message appears in the upper left corner (to short to read). After that, I'm presented the logon screen (all applications are killed).

I've tried to uninstall Gimp, restart and reinstall, but that didn't help. Do you have any advice? Please note that I'm a newby (windows deserter) to Ubuntu.

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Try to open the error console before using any tool. You can access the error console by navigating to Menu -> Windows -> Dockable Dialogs -> Error Console; now use a tool and look if any text appears in the console. If there is any text, we know that something in Gimp itself causes the problem.
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slashcrackJul 15 '12 at 9:46

Alright, I figured out what the problem is: It's the mouse (Nexus Wireless Silent Mouse). Removing its receiver from the USB port and using the Touchpad of my laptop instead solves the problem. Weird, that it only occured in Gimp. Don't know if this question should be closed now. Any advice?
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MatthiasJul 15 '12 at 18:13

I observe the same with my Thinkpad T410s since recently. Did anybody find or create a bug report for this? Some more infos: It crashes or crashes not, depending of me pressing Fn+F8 before that. Fn-F8 changes between Touchpad enabled/disabled. I however always use the touch point.. So the bug is somewhere in X11/input devices.
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alfonxJul 16 '12 at 4:41

Enabling the touchpad solves the issue for me as well (Asus Zenbook).
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Lars NyströmAug 21 '13 at 15:45